1. Field of the Invention
The present invention relates to a surface light source device and a display device using the same.
2. Description of the Background Art
Surface light source devices, which irradiate a rear surface of a display element such as a liquid crystal panel with a light beam to illuminate a display screen from a back surface, include side light type and direct type ones. Light sources are arranged on side surfaces of a casing in the side light type (also referred to as edge light type) surface light source device, while a light source is arranged on a rear surface of a casing by being opposed to a liquid crystal panel in the direct type surface light source device.
Further, the side light type surface light source devices include devices in which a light guide plate is used for guiding a light beam from a light source to an opening of a casing. In a surface light source device using a light guide plate, the light beam emitted from a side light portion including a line light source such as a cold cathode fluorescent lamp (CCFL) or point light sources such as light emitting diodes (LEDs) is reflected within the light guide plate and diffused in a diffusion pattern provided in the light guide plate, to thereby extract the light beam from the opening in a planar manner.
As to a side light type surface light source device using point light sources such as LEDs, for example, Japanese Patent Application Laid-Open No. 08-236814 proposes a surface light source device in which a support separate from a light guide plate is provided to an incident surface of the light guide plate, and LEDs are inserted through through holes provided in the support to be supported by and fixed to the support. It is described that in this surface light source device, LED lamps and the support can be prevented from becoming misaligned by welding or bonding the LED lamps to the support, and accordingly the light guide plate and the LEDs do not become misaligned, which does not impair the efficiency of incidence on the light guide plate.
However, in a conventional surface light source device as described above, a light guide plate and a support for supporting and fixing the LEDs that is provided separately from the light guide plate are provided, and LED lamps and the support are fixed by welding. This causes drawbacks that an interface of a welding portion becomes uneven, leading to diffuse reflection of incident light beams, and that a material for the support is limited in terms of welding and bonding properties for the LED lamps. Further, an insertion groove for inserting an edge of the light guide plate thereinto is provided in the support, where point light sources become misaligned in a case where a light guide plate is deformed, for example, is warped. Moreover, the drawback is that the support needs to be used for fixing the LEDs, which increases the number of components and makes the assembly more difficult.